Should the +4 Locomotive cards found in TtR:Marklin be usable to move Alvin or Dexter, or only the normal Locomotive cards?

Or, might it most be in the spirit of the rules to prohibit using the +4 Locomotive cards singly to move a monster three cities, but allow them as part of playing two Locomotives at once to move the monster six cities?

(And could whichever answer is correct be added to the FAQ for Alvin & Dexter?)